Method of forming an electronic structure using reforming gas, system for performing the method, and structure formed using the method

ABSTRACT

Methods of and systems for reforming films comprising silicon nitride are disclosed. Exemplary methods include providing a substrate within a reaction chamber, forming activated species by irradiating a reforming gas with microwave radiation, and exposing substrate to the activated species. A pressure within the reaction chamber during the step of forming activated species can be less than 50 Pa.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims priority to, U.S. patentapplication Ser. No. 16/896,238, filed Jun. 9, 2020, and titled METHODOF FORMING AN ELECTRONIC STRUCTURE using reforming gas, SYSTEM FORPERFORMING THE METHOD, AND STRUCTURE FORMED USING THE METHOD, whichclaims the benefit of U.S. Provisional Patent Application No. 62/860,158filed on Jun. 11, 2019, the disclosures of which are incorporated hereinin their entirety by reference.

FIELD OF INVENTION

The present disclosure generally relates to methods of treating materialon a surface of a substrate, to structures formed using the method, andto systems for treating the material.

BACKGROUND OF THE DISCLOSURE

Conformal film deposition may be desirable for a variety of reasons. Forexample, during the manufacture of devices, such as semiconductordevices, it is often desirable to conformally deposit material overfeatures formed on the surface of a substrate. Such techniques can beused for shallow trench isolation, inter-metal dielectric layers,passivation layers, and the like. However, with miniaturization ofdevices, it becomes increasingly difficult to conformally depositmaterial, particularly over high aspect ratio features, such as featureshaving an aspect ratio of three or more.

Atomic layer deposition (ALD) can be used to conformally depositmaterial onto a surface of a substrate. For some applications, such aswhen precursors and/or reactants otherwise require a relatively hightemperature for ALD deposition and/or when it is desired to keep aprocessing temperature relatively low, it may be desirable to useplasma-enhanced ALD (PE-ALD).

Unfortunately, material deposited using PE-ALD can exhibit relativelypoor film quality—e.g., exhibit a relatively high etch rate in a liquidor gas-phase etchant. For example, silicon nitride films deposited usingPE-ALD can exhibit relatively high etch rates in dilute hydrofluoricacid (e.g., 1:100 by volume HF:H₂O), compared to silicon nitride filmsdeposited without the aid of a plasma. Efforts to improve low quality ofPE-ALD deposited material have focused on tuning deposition parameters,such as RF power, plasma exposure time, pressure, as well as precursorsused to deposit the material. However, such techniques may not producedesired film quality and/or film uniformity, particularly along adimension (e.g., height) of a feature including the film.

Accordingly, improved methods for forming high-quality material, such assilicon nitride, on a substrate and structures formed using such methodsare desired. Any discussion of problems and solutions described in thissection has been included solely for the purposes of providing a contextfor the present invention and should not be taken as an admission thatany or all of the discussion was known at the time the invention wasmade.

SUMMARY OF THE DISCLOSURE

Various embodiments of the present disclosure relate to methods offorming high-quality films using PE-ALD. While the ways in which variousembodiments of the present disclosure address drawbacks of prior methodsand systems are discussed in more detail below, in general, variousembodiments of the disclosure provide improved methods that include areforming step to improve a quality of a deposited film.

In accordance with at least one embodiment of the disclosure, a methodof forming an electronic device structure includes providing a substratewithin a reaction chamber, forming activated species by irradiating areforming gas with microwave radiation, and exposing a layer comprisingsilicon nitride to the activated species. A pressure within the reactionchamber during the step of forming activated species can be less than 50Pa. The layer comprising silicon nitride can be deposited overlyingfeatures (e.g., trenches or protrusions, such as fins) formed on thesurface of the substrate. The reforming gas can include hydrogen and oneor more of helium and argon. The reforming gas can also include anitrogen source gas, such as one or more of the group consisting of N₂and NH₃. By way of examples, the reforming gas can comprise, consist of,or consist essentially of hydrogen, optionally a nitrogen source gas,and one or more of helium and argon. An amount of helium, hydrogen,and/or argon in the reforming gas can each range from about 5% to about95%, about 20% to about 70%, 40% to about 60%, or be about 50% byvolume. The reforming gas comprises 0% or greater than 0% and less than10% or less than 5% by volume of nitrogen source gas. The microwaveradiation can be emitted from an antenna (e.g., a pole-type antenna)provided above the susceptor in the reaction space. The methodsdescribed herein can be used to form layers deposited in the manufactureof 3D NAND and/or Fin-FET devices.

In accordance with yet further exemplary embodiments of the disclosure,a deposition apparatus configured to perform a method as describedherein is provided.

In accordance with yet further exemplary embodiments of the disclosure,a structure comprises a layer formed according to a method describedherein.

These and other embodiments will become readily apparent to thoseskilled in the art from the following detailed description of certainembodiments having reference to the attached figures; the invention notbeing limited to any particular embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

A more complete understanding of exemplary embodiments of the presentdisclosure can be derived by referring to the detailed description andclaims when considered in connection with the following illustrativefigures.

FIG. 1 illustrates a reactor system in accordance with at least oneembodiment of the disclosure.

FIG. 2 illustrates a method of forming a structure in accordance with atleast one embodiment of the disclosure.

FIGS. 3-6 illustrate wet etch rate ratios (WERR) to TOX of PE-ALDdeposited silicon nitride films in dilute (1:100) HF acid under variousconditions in accordance with exemplary embodiments of the disclosure.

FIG. 7 illustrates thickness of a layer comprising silicon nitride(e.g., SiN) as a function of depth in a feature.

FIG. 8 illustrates thickness at the top of a feature (depth=0) as afunction of He:H concentration during a reforming step.

FIGS. 9 and 10 illustrate wet etch rate ratios (WERR) of PE-ALDdeposited silicon nitride films in dilute (1:100) HF acid under variousconditions in accordance with exemplary embodiments of the disclosure.

FIG. 11 illustrates damage near a surface of a feature as a function ofhydrogen in the hydrogen/argon reforming gas.

It will be appreciated that elements in the figures are illustrated forsimplicity and clarity and have not necessarily been drawn to scale. Forexample, the dimensions of some of the elements in the figures may beexaggerated relative to other elements to help improve understanding ofillustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it willbe understood by those in the art that the invention extends beyond thespecifically disclosed embodiments and/or uses of the invention andobvious modifications and equivalents thereof. Thus, it is intended thatthe scope of the invention disclosed should not be limited by theparticular disclosed embodiments described below.

The present disclosure generally relates to methods of formingelectronic device structures, to deposition apparatus for performing themethods, and to structures formed using the method. By way of examples,the systems and methods described herein can be used to formhigh-quality silicon nitride films. The silicon nitride films can bedeposited (e.g., conformally) using PE-ALD onto a surface of asubstrate, which can include high-aspect ratio features. The PE-ALDdeposited material can then be exposed to activated species formed byirradiating a reforming gas with microwave radiation to form a structureincluding high-quality silicon nitride films.

In this disclosure, “gas” may include material that is a gas at roomtemperature and pressure, a vaporized solid and/or a vaporized liquid,and may be constituted by a single gas or a mixture of gases, dependingon the context. A gas other than the process gas, i.e., a gas introducedwithout passing through a gas distribution assembly, such as ashowerhead, other gas distribution device, or the like, may be used for,e.g., sealing the reaction space, which includes a seal gas, such as arare gas. In some embodiments, the term “precursor” refers generally toa compound that participates in the chemical reaction that producesanother compound, and particularly to a compound that constitutes a filmmatrix or a main skeleton of a film, whereas the term “reactant” refersto a compound, other than precursors, that activates a precursor,modifies a precursor, or catalyzes a reaction of a precursor, whereinthe reactant may provide an element (such as O, N, C) to a film matrixand become a part of the film matrix, when, for example, RF power isapplied. The term “inert gas” refers to a gas that does not take part ina chemical reaction and/or a gas that excites a precursor when RF poweris applied, but unlike a reactant, it may not become a part of a filmmatrix to an appreciable extent.

“Reforming gas” can refer to a gas used for post-deposition treatment orintroduced to the reaction space during post-deposition treatment. Insome cases, the reforming gas does not include precursor, reactant,and/or additive gas used for deposition gas to deposit material that isbeing reformed by the reforming gas. The reforming gas may include aseal gas, other inert gas, or other additive gas. When the reforming gasis constituted by multiple gases, it can be introduced as a mixed gas orseparately to a reaction space. The reforming gas can be introduced tothe reaction space through a shower plate or other gas inflow port whichis capable of feeding the gas uniformly to the reaction space oruniformly around an antenna for generating a direct microwave plasmainstalled in the reaction space. The reforming gas may be introduced tothe reaction space upstream of the antenna or toward a surface of theantenna facing the susceptor.

As used herein, the term “substrate” may refer to any underlyingmaterial or materials that may be used to form, or upon which, a device,a circuit, or a film may be formed. A substrate can include a bulkmaterial, such as silicon (e.g., single-crystal silicon), other Group IVmaterials, such as germanium, or compound semiconductor materials, suchas GaAs, and can include one or more layers overlying or underlying thebulk material. Further, the substrate can include various topologies,such as recesses, lines, and the like formed within or on at least aportion of a layer of the substrate.

In some embodiments, “film” refers to a layer continuously extending ina direction perpendicular to a thickness direction substantially withoutpinholes to cover an entire target or concerned surface, or simply alayer covering a target or concerned surface. In some embodiments,“layer” refers to a structure having a certain thickness formed on asurface or a synonym of film or a non-film structure. A film or layermay be constituted by a discrete single film or layer having certaincharacteristics or multiple films or layers, and a boundary betweenadjacent films or layers may or may not be clear and may or may not beestablished based on physical, chemical, and/or any othercharacteristics, formation processes or sequence, and/or functions orpurposes of the adjacent films or layers.

As used herein, the term “atomic layer deposition” (ALD) may refer to avapor deposition process in which deposition cycles, typically aplurality of consecutive deposition cycles, are conducted in a processchamber. Typically, during each cycle, the precursor is chemisorbed to adeposition surface (e.g., a substrate surface or a previously depositedunderlying surface such as material from a previous ALD cycle), forminga monolayer or sub-monolayer that does not readily react with additionalprecursor (i.e., a self-limiting reaction). Thereafter, a reactant(e.g., another precursor or reaction gas) may subsequently be introducedinto the process chamber for use in converting the chemisorbed precursorto the desired material on the deposition surface. Typically, thisreactant is capable of further reaction with the precursor. Further,purging steps may also be utilized during each cycle to remove excessprecursor from the process chamber and/or remove excess reactant and/orreaction byproducts from the process chamber after conversion of thechemisorbed precursor. Further, the term “atomic layer deposition,” asused herein, is also meant to include processes designated by relatedterms, such as chemical vapor atomic layer deposition, atomic layerepitaxy (ALE), molecular beam epitaxy (MBE), gas source MBE, ororganometallic MBE, and chemical beam epitaxy when performed withalternating pulses of precursor composition(s), reactive gas, and purge(e.g., inert carrier) gas. PE-ALD refers to an ALD process, in which aplasma is applied during one or more of the ALD steps.

As used herein, the term “a layer comprising silicon nitride” refers toa layer that includes silicon and nitrogen. Unless otherwise noted, alayer comprising silicon nitride can include additional elements, suchas oxygen and/or carbon. By way of examples, a layer comprising siliconnitride can include SiNx, where x ranges from about 1 to about 1.33, orSiOCN films.

Further, in this disclosure, any two numbers of a variable canconstitute a workable range of the variable as the workable range can bedetermined based on routine work, and any ranges indicated may includeor exclude the endpoints. Additionally, any values of variablesindicated (regardless of whether they are indicated with “about” or not)may refer to precise values or approximate values and includeequivalents, and may refer to average, median, representative, majority,etc. in some embodiments. Further, in this disclosure, the terms“constituted by” and “having” refer independently to “typically orbroadly comprising,” “comprising,” “consisting essentially of,” or“consisting of” in some embodiments. In this disclosure, any definedmeanings do not necessarily exclude ordinary and customary meanings insome embodiments.

In this disclosure, “continuously” can refer to one or more of withoutbreaking a vacuum, without interruption as a timeline, without anymaterial intervening step, without changing treatment conditions,immediately thereafter, as a next step, or without an interveningdiscrete physical or chemical structure between two structures otherthan the two structures in some embodiments.

Turning now to the figures, FIG. 1 illustrates a system 100 for formingan electronic device structure as described herein. System 100 includesa reaction chamber 102 and a plasma-generating chamber 104 disposedabove reaction chamber 102, wherein an interior region 106 of reactionchamber 102 is in fluid communication with an interior region 108 ofplasma-generating chamber 104. System 100 further includes a susceptor110, which, in the illustrated example, is capable of moving verticallyto load and unload a substrate 112. Lift pins 114 and a robot arm (notshown) can be used to load and unload the substrate from the surface ofsusceptor 110. When susceptor 110 is at an upper position or processingposition, interior region 106 (or reaction space) of the reactionchamber 102 is separated from a loading/unloading section 116 by anisolation ring 118. The reaction space 106 can be evacuated via anannular exhaust duct 120.

During operation of system 100, a reforming gas and/or other gas can besupplied to the reaction space 106 from the plasma-generating chamber104. In the illustrated example, plasma-generating chamber 104constitutes a plasma-generating section 122 right above the reactionspace 106. An antenna, such as a pole-type microwave antenna 124 can bedisposed facing substrate 112 and can be parallel to susceptor 110, sothat microwaves can be uniformly transmitted toward the substrate whilethe reforming gas is fed to the plasma-generating chamber 104 (e.g., inthe direction of arrows 126). The pole-type microwave antenna 124 can beprovided with and connected to magnetrons (not shown) typically attachedat the ends of antenna 124 to feed microwaves into antenna 124.

In some embodiments, the pole-type microwave antenna is enclosed in aquartz or ceramic tube which functions as a microwave window, wherein aplasma grows from both ends and extends along the tube, thereby formingan axially-homogeneous microwave plasma. Multiple pole-type microwaveantennas (e.g., 2, 4, or 8) can be installed in parallel to each otherto form a two-dimensional plasma array for forming a uniform plasma withreference to a surface of substrate 112. Since a microwave plasma is adirect microwave plasma, no magnetic coil may be used (i.e., no magneticfield formed to generate a plasma). Further, no bias voltage may besupplied to the susceptor 110, so as to prevent ion energy from becomingtoo high and causing damage to the film or etching of the film.Alternatively, a slot antenna (a plate-type antenna with multiple slots)can be used to generate a surface wave plasma, wherein a shower platefor feeding a reforming gas to the reaction space is installed above theslot antenna at a short distance (upstream of the slot antenna). Anyother microwave antennas, including conventional antennas, suitable forgenerating a direct microwave plasma can be used. The direct microwaveplasma which contains both radicals and ions is different from a remoteplasma which contains primarily radicals and substantially no ions.

System 100 can include one or more controller(s) 128 programmed orotherwise configured to cause the reforming or other steps describedherein. Controller(s) 128 can be communicated with the various powersources, heating systems, pumps, robotics and gas flow controllers orvalves of the reactor.

FIG. 2 illustrates a method 200 in accordance with additionalembodiments of the disclosure. Method 200 includes the steps ofproviding a substrate within a reaction chamber (step 202), formingactivated species by irradiating a reforming gas with microwaveradiation (step 204), and exposing a layer comprising silicon nitride tothe activated species (step 206). In some embodiments, method 200 isconducted during a process of forming a 3D NAND device or a Fin-FETdevice.

During step 202, the substrate provided within the reaction chamber caninclude features, such as trenches, vias, or protrusions. The substratecan further include a layer comprising silicon nitride overlying thefeatures. One or more features can have a width of about 10 nm to about100 nm, a depth or height of about 30 nm to about 1000 nm, and/or anaspect ratio of about 3 to 100 or about 3 to about 20.

In some cases, the substrate includes features, wherein the layercomprising silicon nitride may have inferior quality (e.g., higher wetetch rates) at sidewalls of the features as compared with a quality ofthe layer comprising silicon nitride, at, for example, a top surface ofthe feature.

During step 202, the substrate can be brought to a desired temperatureand pressure for subsequent processing. By way of examples, a substratetemperature or a temperature of a susceptor can be brought to atemperature of about 20° C. to about 400° C. or 140° C. to 260° C. Apressure within the reaction chamber during the step of formingactivated species is less than 50 PA or between about 1 Pa to about 30Pa or about 0.1 Pa to less than 50 Pa.

In some embodiments, step 202 includes depositing the silicon nitridefilm on the substrate by plasma-enhanced ALD (PE-ALD) in a PE-ALDapparatus, and then transferring the substrate to the reaction space ina microwave plasma apparatus without exposing the substrate to air.Silicon nitride is relatively chemically stable and thus, exposure ofthe silicon nitride film to air before the reforming step may not causea problem; however, when the silicon nitride film is very thin, e.g., athickness is approximately 3 nm, oxidation of an exposed surface of thefilm may affect the property of a final product or the operation ofsubsequent processes. In this case, a PE-ALD apparatus and a microwaveplasma apparatus (e.g., used for deposition of the silicon nitride file)can be installed within the same module and connected via a back-endrobot. This way, the substrate can be transferred from the PE-ALDapparatus to the microwave plasma apparatus without exposing thesubstrate to air.

In some embodiments, the silicon nitride film is deposited by PE-ALDsince PE-ALD is capable of depositing a film with high conformality(e.g., 80% to 100%, preferably 90% or higher, wherein the conformalityis defined as a ratio (%) of thickness of film at the center of asidewall of a trench to thickness of film at the center of a top surfaceon which the trench is formed) at a relatively low temperature (e.g.,400° C. or lower). However, other processes, such as thermal ALD orLPCVD, can be used to deposit a silicon nitride film by using arelatively high temperature (e.g., 600° C. or higher). An exemplaryPE-ALD process can include exposing the substrate to a siliconprecursor, such as silane, halogensilane (diclorosilane, diiodosilane,hexachlorodisilane, octachlorotrisilane), organosilane(tris(dimethylamino)silane, Bis(tert-butylamino)silane,di(sec-butylamino)silane), and heterosilane (trisilylamine,neopentasilane), purging the reaction chamber, expositing the substrateto activated nitrogen species formed by exposing a nitrogen-containinggas (e.g., nitrogen source gas), such as nitrogen, for example, to radiofrequency radiation, purging the reaction chamber, and repeating thesesteps until a desired thickness of a layer comprising silicon nitride isobtained.

During step 204, activated species are formed by irradiating a reforminggas with microwave radiation. A pressure and temperature within areaction space during step 204 can be the same or similar to thetemperature and pressure within the reaction space during step 202.

In some embodiments, the microwaves have a frequency of 800 MHz to 10GHz. Since microwaves have a significantly higher frequency than an RFfrequency (typically 13.56 MHz), a plasma having a high density can begenerated using microwaves. For example, a cut-off frequency (f [Hz])can be calculated as f≈9·√(ne) wherein ne is a plasma density [/m³]. Ifthe cut-off frequency is 13.56 MHz, the plasma density is approximately2×1012/m³, whereas if the cut-off frequency is 2.45 GHz, the plasmadensity is approximately 4×1016/m³, indicating that electric power canbe supplied to a plasma until the plasma density reaches a significantlyhigher level when using microwaves than when using RF waves, i.e.,microwaves are more effective than RF waves as a plasma source. Further,electron temperature obtained when using microwaves is lower than thatobtained when using RF waves. Additionally, ions follow RF waves andswing, whereas ions do not follow microwaves and thus do not swing. Theexcited state of atoms and molecules by microwaves is different fromthat by RF waves.

The plasma density is also referred to as “electron density” or “ionsaturation current density” and refers to the number of free electronsper unit volume. The plasma density in the reaction space can bemeasured using a Langmuir probe (e.g., LMP series).

By using microwaves (having an ultra-high frequency of typically 800 MHzor higher), the plasma density can be increased (for example, the plasmadensity of a microwave (2.45 GHz) plasma is at least one to two digitshigher than that of an RF (13.56 MHz) plasma, and electron temperatureof the microwave plasma is a half or less of that of the RF plasma).

In some embodiments, in order to generate a homogeneous or uniformplasma in the reaction space, an antenna, such as antenna 124, isprovided away from the susceptor at a distance of about 5 cm to about 10cm between the antenna and the susceptor. In some embodiments, asusceptor, such as susceptor 110, is continuously or intermittently(e.g., rotating the susceptor by 90° once or multiple times) rotatedduring step 204 to facilitate formation of a homogeneous or uniformplasma within a reaction space.

In some embodiments, microwave power of emitting the microwaves isbetween about 500 W and about 10,000 W (preferably, between about 1,000W and about 3,000 W). The above-indicated power is for a 300-mm waferand can be converted to W/cm² (wattage per unit area of a wafer) as 0.71W/cm² to 14.15 W/cm² (preferably 1.41 W/cm² to 4.24 W/cm²) which canapply to a wafer having a different diameter such as 200 mm or 450 mm.

In some embodiments, the reforming gas can include hydrogen and/orhelium. For example, the reforming gas can be helium or include about0.1% to about 99.9% by volume of He. In some embodiments, the reforminggas can include about 0.1% to about 99.9% by volume of He. In someexamples, the reforming gas can include hydrogen and one or more ofhelium and argon. By way of examples, the reforming gas contains about5% to about 95%, about 20% to about 70% by volume, or about 40% to about60% by volume of He. Additionally or alternatively, the reforming gascan include about 5% to about 95%, about 20% to about 70% by volume, orabout 40% to about 60% by volume of Ar. An amount of hydrogen in thereforming gas can range from about 5% to about 95%, about 20% to about70% by volume, or about 40% to about 60% by volume.

The reforming gas can also include a nitrogen source gas, such as of N₂and/or NH₃. The reforming gas can include no nitrogen source gas or fromgreater than 0% and to less than 10% by volume or from greater than 0%and to less than 5% by volume of nitrogen source gas.

In some embodiments, only the reforming gas is supplied to the reactionspace during step 204—i.e., no precursor nor reactant gas is supplied tothe reaction space during this step. Further, during step 204, no filmis deposited on the substrate, i.e., the thickness of the siliconnitride film is not increased; in some embodiments, the thickness of thesilicon nitride film may be decreased (e.g., by approximately 3 nm) dueto the etching effect of excited reforming gas (generating, e.g., ahydrogen plasma). Typically, the thickness of the silicon nitride filmdoes not change substantially during the reforming step.

Although separately illustrated, steps 204 and 206 can occur atsubstantially the same time. A pressure and temperature within areaction chamber during step 206, also referred to herein as a reformingstep, can be the same or similar to the pressure and temperature notedabove in connection with steps 202 and 204.

Table 1 below illustrates exemplary process conditions for steps 202-206of method 200.

TABLE 1 Conditions for Step 204 Pressure >0 to <50 Pa (of 0.1 to 30 Pa)Substrate temperature 20 to 400° C. (or 50 to 250° C.) Reforming gas He,H₂, He + H₂, Ar + H₂ (all with or without a nitrogen source gas) Flowrate of reforming gas 1 to 1000 sccm (or 10 to 100 sccm) (continuous)Frequency of microwaves 0.9 to 10 GHz (or 0.9 to 5.8 GHz) Microwavepower for a 300-mm 500 to 10,000 W (or 1,000 to 3,000 W) wafer Distancebetween antenna and 50 to 300 mm (or 50 to 100 mm) susceptor (athickness of a substrate is about 0.7 mm) Duration of reformation step0.1 to 30 min. (or 3 to 10 min.)

The above-indicated microwave power for a 300-mm wafer can be convertedto W/cm² (wattage per unit area of a wafer) which can apply to a waferhaving a different diameter such as 200 mm or 450 mm. The substratetemperature can be considered to be a temperature of the reaction spaceduring the film reformation.

During steps 204 and 206, by irradiating the reforming gas withmicrowaves at a low pressure (e.g., less than 50 Pa), a reforming gasplasma can be generated, which is highly effective in reforming thesilicon nitride film including any portions of the film deposited on thesidewalls of features, thereby realizing the silicon nitride film havingsubstantially uniform or homogeneous quality regardless of locations(e.g., along a height of a feature) of the silicon nitride film. Forexample, the silicon nitride film can have geographically ortopologically substantially uniform or homogeneous quality (e.g., avariation of the etched quantity) in a preset duration of wet etching orper unit of time depending on the geographical or topological locations,e.g., top surface, sidewall, and bottom, may be ±30% or less, typically±20% or ±10% or ±5% less with reference to the average etched quantityat the locations for the aspect ratios noted herein.

In some embodiments, the silicon nitride film has a thickness of 3 nm ormore, and step 206 can continue until the silicon nitride film isreformed from its surface to a depth of 3 nm or more. Reforming thesilicon nitride can be conducted by desorbing and releasing hydrogen andhalogen (if included in the precursor) from the silicon nitride film,and the content of hydrogen and halogen at a portion of the siliconnitride film is indicative of accomplishment of reformation of theportion, i.e., by analyzing the content of hydrogen and halogen in athickness direction, it can be determined to what depth the film isreformed. In some embodiments, when the silicon nitride film is reformedfrom its surface to a depth of 3 nm or more, the reforming effect isconsidered to be sufficient to improve the film quality, such as havinghigh resistance to chemicals (which can be evaluated by WERR). When thesilicon nitride film has a thickness of, for example, 10 nm or more andif it is desired to reform the film from its surface to a depth of 10 nmor more, the reforming step may be repeated after every 10 nm ofaccumulated deposition of the film or after a predetermined number ofdeposition cycles. However, in some cases, since a direct microwaveplasma can penetrate the film from its surface to a depth of more than10 nm, e.g., approximately 40 nm, by manipulating process parametersincluding the reforming step duration, pressure, temperature, andmicrowave power, the film may be reformed in its entirety withoutrepeating the deposition step and reforming step.

FIGS. 3-11 illustrate various examples of the disclosure. These examplesare not intended to limit the present invention. In the examples, whereconditions and/or structures are not specified, the skilled artisan inthe art can readily provide such conditions and/or structures, in viewof the present disclosure, as a matter of routine experimentation. Also,the numbers applied in the specific examples can be modified by a rangeof at least ±50% in some embodiments, and the numbers are approximate.

Unless otherwise noted, the samples for the examples included featureshaving an aspect ratio of about 5.5, with a bottom depth of about 330nm. The samples were etched for about 2.5 minutes. “AsDEP” in thefigures refers to films that were not exposed to a reforming process.Depth refers to a depth within a feature (trench). The silicon nitridefilms were deposited using the following conditions.

TABLE 2 Conditions for depositing SiN film Exemplary Range ExemplaryValue Precursor diiodosilane feed (sccm) Reactant H₂ feed (slm) 0 to 0.10 Reactant N₂ feed (slm) 1 to 10 10 Carrier N₂ feed (slm) 1 to 8 4Sealing N₂ feed (slm) 0.05 to 0.3 0.2 Pressure (Pa) 300 to 4000 3000 RF(13.56 MHz) (W) 100 to 1000 880 Susceptor temperature (° C.) 100 to 400250 Shower head temperature (° C.) 100 to 200 180 Chamber walltemperature (° C.) 100 to 180 150 Electrode gap (mm) 8 to 15 10 Feedtime (sec.) 0.1 to 3 0.3 Purge time (once) (sec.) 0.5 to 3 1.0 Cyclenumber 800 (numbers are approximate)

FIGS. 3-6 illustrate wet etch rate ratios (WERR) of PE-ALD depositedsilicon nitride films in dilute (1:100) HF acid. As illustrated in FIG.3 , for reforming a silicon nitride film using hydrogen, from pressuresranging from 20 Pa to 300 Pa, no WERR improvement was observed at areaction chamber pressure of 300 Pa. At 50 Pa, WERR was improved near asurface of the features, but not at depths extending beyond 120 nm. At apressure of 20 Pa, WERR improvement reached the bottom of the feature.

FIG. 4 illustrates WERR as a function of pressure when using helium as areforming gas.

FIG. 5 illustrates the effect of hydrogen addition to helium reforminggas at a given pressure (20 Pa) and power (2kW) at various depths of afeature. As illustrated, the addition of hydrogen to the reforming gassignificantly improved the WERR of the silicon nitride films, with aHe:H ratio of about 50:50 showing the most improvement in WERR for theseconditions.

FIG. 6 illustrates WERR at various feature depths as a function of He:Hratios. As illustrated, WERR is improved over a wide range of He:Hratios (e.g., from about 5% to about 95% by volume of hydrogen) with themost improvement in the range of about 40% to about 60% hydrogen/helium.

FIG. 7 illustrates thickness of a layer comprising silicon nitride(e.g., SiN) as a function of depth in a feature. The thickness reductioncan correspond to damage caused by the microwave plasma. FIG. 8illustrates thickness at the top of a feature (depth=0) as a function ofHe:H concentration during a reforming step. FIG. 8 illustrates that areforming gas including a combination of helium and hydrogen exposed tomicrowave radiation causes a reduction of the thickness of the layercomprising silicon nitride at the top of the features/pattern.

TABLE 3 Gas Time[min] Ini[nm] Aft[nm] Diff[nm] He:H₂ = 50:50 10 5.5074.7607 −0.7463 He:H₂:N₂ = 49:49:2 10 5.499 5.5109 0.0119 He:H₂:N₂ =49:49:2 10 5.496 5.0662 −0.4298

Table 3 illustrates that the addition of a nitrogen source gas to thereforming gas as described herein can suppress the reduction of thethickness of the layer comprising silicon nitride during a reformingprocess.

FIGS. 9-11 illustrate a WERR and thickness reduction at the top of afeature for a reforming gas that includes argon (rather than helium) andhydrogen. FIG. 9 illustrates that the combination of argon and heliumimproves the WERR, relative to the as-deposited films. FIG. 10illustrates an effect of argon and hydrogen concentration on WERR of aPE-ALD silicon nitride film, and that for a given set of conditions(pressure of 20 Pa and microwave power of 2 kW), a concentration ofabout 30% by volume of hydrogen in argon showed the most improvement inWERR of the films comprising silicon nitride. FIG. 11 illustrates thatdamage near a surface of a feature was reduced as an amount of hydrogenin the hydrogen/argon reforming gas was increased.

FIGS. 3-11 illustrate that low pressure (e.g., less than 50 Pa) and useof a microwave plasma can reform films comprising silicon nitride alonga depth (e.g., to 300 nm or more) of a feature. Helium alone did notappreciably improve WERR along a depth of a feature. This is thought tobe due to Si—N bond breaking. On the other hand, activated speciesformed with helium reach deep areas along a length of a feature. H₂improves WERR, but the effect is diminished along a depth of a feature.A combination of He (and/or argon) and H₂ dramatically improves WERR atdeep areas of a feature. This is thought to be due to helium and/orargon making it easier to penetrate hydrogen radicals in the SiN film.Damage of the top of the pattern/feature is thought to be primarily dueto selective sputtering of N atoms. N atoms are preferentially sputteredby He or H₂ ions than Si atoms, because momentum transfer is moreeffective in N atoms due to atomic mass ratio. Addition of nitrogensource gas can be effective to reduce the damage, because the selectivesputtering is compensated with N adsorption.

The example embodiments of the disclosure described above do not limitthe scope of the invention, since these embodiments are merely examplesof the embodiments of the invention. Any equivalent embodiments areintended to be within the scope of this invention. Indeed, variousmodifications of the disclosure, in addition to those shown anddescribed herein, such as alternative useful combinations of theelements described, may become apparent to those skilled in the art fromthe description. Such modifications and embodiments are also intended tofall within the scope of the appended claims.

What is claimed is:
 1. A method of forming an electronic devicestructure, the method comprising: providing a substrate on a susceptorwithin a reaction chamber, the substrate having features thereon andcomprising a layer comprising silicon nitride overlying the features;providing a pole-type antenna above the susceptor, the pole-type antennaextending across two sides of the reaction chamber and positionedparallel to the susceptor; forming activated species by irradiating areforming gas with microwave radiation emitted from the pole-typeantenna; and exposing the layer comprising silicon nitride to theactivated species.
 2. The method according to claim 1, wherein thereforming gas comprises hydrogen and one or more of helium and argon. 3.The method according to claim 1, wherein the reforming gas compriseshydrogen and helium.
 4. The method according to claim 1, wherein thereforming gas comprises a nitrogen source gas.
 5. The method accordingto claim 4, wherein the nitrogen source gas is selected from one or moreof the group consisting of N₂ and NH₃.
 6. The method according to claim1, wherein the reforming gas consists essentially of hydrogen, anitrogen source gas, and one or more of helium and argon.
 7. The methodaccording to claim 1, wherein the reforming gas comprises about 5% toabout 95% by volume of He.
 8. The method according to claim 1, whereinthe reforming gas comprises about 20% to about 70% by volume of He. 9.The method according to claim 1, wherein the pole-type antenna isenclosed in a tube, the tube comprising quartz or ceramic.
 10. Themethod according to claim 1, wherein the reforming gas comprises about40% to about 60% by volume of H.
 11. The method according to claim 1,wherein the reforming gas comprises greater than 0% and less than 10% byvolume of nitrogen source gas.
 12. The method according to claim 1,further comprising providing at least one additional pole-type antennaabove the susceptor, wherein the pole-type antennas are providedparallel to each other.
 13. The method according to claim 1, wherein themicrowave radiation has a frequency of about 800 MHz to about 10 GHz.14. The method according to claim 1, wherein a microwave power emittingthe microwave radiation is between about 500 W and about 10,000 W. 15.The method according to claim 1, wherein the pole-type antenna isprovided at a distance of about 5 cm to about 10 cm from the susceptor.16. The method according to claim 1, wherein no RF power is supplied tothe susceptor during the step of forming activated species.
 17. Themethod according to claim 1, wherein the pressure within the reactionchamber during the step of forming activated species is between about 1Pa and about 50 Pa.
 18. The method according to claim 1, wherein atemperature of a susceptor within the reaction chamber during the stepof forming activated species is between about 20° C. and about 400° C.19. The method according to claim 1, further comprising a step ofdepositing the silicon nitride film on the substrate by plasma-enhancedatomic layer deposition (PE-ALD) in a PE-ALD apparatus, and thentransferring the substrate to a reaction space in a microwave plasmaapparatus without exposing the substrate to air.
 20. A system forperforming the method of claim 1.